1. Field of Endeavor
The present invention relates generally to laser drilling, and more particularly to a method and apparatus for drilling a hole.
2. State of Technology
U.S. Pat. No. 6,172,331 for a method and apparatus for laser drilling by Xiangli Chen, patented Jan. 9, 2001, states, “Lasers are commonly used to drill holes in materials. In the aerospace and power generation industries for example, lasers are commonly used to drill air cooling holes in turbine airfoils such as blades and vanes. A pulsed laser beam is directed at the article, and molten material from the focus region of the laser beam is expelled from the article. According to one known method, a Nd:YAG laser generates pulses having a pulse energy of 10 joules, a pulse duration of 1 millisecond, and a pulse repetition rate of 10 Hz, to drill holes in hollow turbine blades. The pulses are generated in a “free running” mode in which the lamps are pulsed at 10 Hz to produce the pulsed laser beam.”
The article, “Precision Micromachining with Pulsed Green Lasers,” by Jim J. Chang, Bruce E. Warner, Ernest P Dragon, and Mark W. Martinez, Journal of Laser Applications, Vol. 10, No. 6, pages 285-321, Dec. 1998, states “Laser micromachining has found expanded use in automobile, aerospace, and electronics industries.”
U.S. Pat. No, 4,870,244 for a method and device for stand-off laser drilling and cutting, by John Q. Copley et al, patented Sep. 26, 1989 shows a device for perforating material and a method of stand-off drilling using a laser. In its basic form a free-running laser beam creates a melt on the target and then a Q-switched short duration pulse is used to remove the material through the creation of a laser detonation wave. The advantage is a drilling/cutting method capable of working a target at lengthy stand-off distance. The device may employ 2 lasers or a single one operated in a free-running/Q-switched dual mode. Applicants believe that a disadvantage of this method is that with the high energy of the free running laser which produces the melt zone, there may be a large HAZ which may reduce the strength of the material surrounding the hole. Also, the dimension precision of the hole is likely to be poor.
U.S. Pat. No. 5,741,096 for a line-laser assisted alignment apparatus, by Stephen P. Olds, patented Apr. 21, 1998 shows a line laser assisted alignment apparatus that uses two laser line generators to define a reference axis that is aligned to coincide with an axis of a drill bit or other rotational tool. The reference axis of the alignment apparatus is matched with a marked position on a lower surface of an object that is to be worked by the drill bit or other rotational tool. Applicants believe that this technique improves the dimensional tolerance of the holes by aiding in the alignment process but is not involved with the other important features of precision hole drilling such as deep aspect ratios and minimal HAZ.